1. Field of the Invention
The present invention relates to a data stream conversion apparatus and method for converting a stream of variable length data to a stream of fixed length data of a predetermined bit length, a variable length coded data stream generation apparatus and method using the data stream conversion apparatus and method for example for JPEG and other variable length coding and efficiently generating a predetermined data stream, and a camera system coding the signal of a captured image by variable length coding.
2. Description of the Related Art
As an internationally standardized system for compressing and coding still picture data, there is known the JPEG (color still image coding system of the Joint Photographic Experts Group). As an internationally standardized system for compressing and coding moving picture data, there is known the MPEG (moving picture coding system of the Moving Picture Coding Experts Group).
One of the systems in broad use as a system for compressing and coding images including these systems is DCT (discrete cosine transform). The standard flow of processing in the DCT coding system is to divide the input image to 8xc3x978 pixel blocks, process the block units by DCT, quantize the obtained DCT coefficients, and code them by variable length coding. Huffman coding etc. are used for the coding at this time.
In this way, for efficient coding, the general practice has been to perform variable length coding at the final stage of the coding of the image data. On the other hand, the data format when recording or transmitting or displaying this coded data is usually data of a predetermined bit length, that is, the processing is usually performed on a data stream of units of data of a fixed length. Therefore, it is necessary to convert the generated variable length coded data into data of a predetermined bit length. The processing for conversion of the data format tends to complicate the control and increase the size of the circuit despite being simple processing. There has therefore been a demand for more efficient conversion with simpler control.
Specifically, for example, since the timing of generation of coded data and the timing of reading of the generated coded data differ, the circuits between them have to be used synchronized with a plurality of operating clocks. This complicated the control. As a result, sometimes the input side was asked to wait or the output side was kept in the ready state. That is, operational limits were imposed on the outside. It had therefore been desired to enable use with a simpler interface.
Further, if data is input and output a synchronously, to prevent data overflow or corruption, the tendency has been to design the circuit with a large number of buffers and registers internally. The size of the circuit has therefore become larger. In particular, when configuring such a coding circuit on an LSI, it is desirable to reduce the size of the circuit as much as possible. The size of the conversion circuit has therefore become a problem.
An object of the present invention is to provide a data stream conversion apparatus and method for converting a stream of variable length data to a stream of fixed length data of a predetermined bit length by a smaller size of circuit and a simpler configuration and control.
Another object of the present invention is to provide a variable length coded data stream generation apparatus and method for coding desired data by variable length coding to generate a predetermined data stream by a smaller size of circuit and a simpler configuration and control.
Still another object of the present invention is to provide a camera system for capturing a desired image and coding the captured image by variable length coding which codes the captured image data by variable length coding to efficiently generate an image data stream by a smaller size of circuit and a simpler configuration and control.
According to a first aspect of the present invention, there is provided a data stream conversion apparatus, comprising a first data combining means for successively combining an input variable length data and a data portion not extracted as output data portion in already input data, a data extracting means for successively extracting predetermined data portions of the predetermined data length from the successively combined data as the output data portions, and an output means for successively outputting output data of a predetermined data length based on the successively extracted output data portions.
According to a second aspect of the present invention, there is provided a data stream conversion method, comprising the steps of successively combining an input variable length data with a data portion not extracted as output data portion in already input data, successively extracting predetermined data portions of the predetermined data length from the successively combined data as the output data portions, and successively outputting output data of a predetermined data length based on the successively extracted output data portions.
According to a third aspect of the present invention, there is provided a variable length coded data stream generation apparatus, comprising a variable length coding means for coding desired data by variable length coding, a first data combining means for successively combining the variable length coded data resulting from the variable length coding with a data portion not extracted as output data portion in already coded variable length coded data, a data extracting means for successively extracting predetermined data portions of the predetermined data length from the successively combined variable length coded data as output data portions, and an output means for successively outputting data of a predetermined fixed length based on the successively extracted output data portions.
According to a fourth aspect of the present invention, there is provided a variable length coded data stream generation method, comprising the steps of coding desired data by variable length coding, successively combining the variable length coded data resulting from the variable length coding with data portions not extracted as output data in already coded variable length coded data, successively extracting predetermined data portions of a predetermined data length from the successively combined variable length coded data as output data portions, and successively outputting data of a predetermined fixed length based on the successively extracted output data portions.
According to a fifth aspect of the present invention, there is provided a camera system comprising a capturing means for capturing a desired image and generating image data a variable length coding means for coding the generated image data by variable length coding, a first data combining means for successively combining variable length coded data resulting from the variable length coding with portions not extracted as output data portion in already captured variable length coded data, a data extracting means for successively extracting predetermined portions of a predetermined data length from the successively combined variable length coded data as the output data portions, a data stream generating means for successively generating data of a predetermined fixed length to generate a stream of image data based on the successively extracted output data portions, and a processing means for performing predetermined processing on the generated stream of image data.